Double tapered roller of scroll thrust bearing

ABSTRACT

In double tapered rollers of a thrust scroll bearing, a structure free from generation of edge load at both ends of a section straight line on conical or tapered surfaces, and appropriate in contact stress with the bearing race is presented. To be used as a rolling element of thrust bearing interposed between positions making relative scroll motions, it is a conical body having a pair of conical surfaces (Ra, Rb) matched coaxially and coupled at bottoms mutually, and the entire surface of the conical surfaces (Ra, Rb) is processed by crowning. As a result, edge load is not generated at both ends of the section straight line of the conical surfaces (Ra, Rb), and the maximum contact stress at the apex side is held at a low value within an allowable range.

TECHNICAL FIELD

The present invention relates to double tapered rollers of a scrollthrust bearings, and more particularly to a conical surface shape ofdouble tapered rollers used as rolling elements in a scroll thrustbearing preferably employed, for example, in a thrust force supportstructure in a scroll type compressor.

BACKGROUND ART

The scroll type compressor is a kind of rotary compressors, and fluidcompression is continuous, and as compared with the conventionalreciprocating compressors, torque fluctuations and vibrations are smalland high speed operation is possible, and hence it is recently appliedwidely.

This kind of compressor has a thrust force support structure forenabling scroll driving. This support structure is a so-called built-intype integrally incorporated in the compressor, but forms a kind ofthrust bearing, and a bearing known as ball coupling used in suchposition has been already known as an independent machine element.

Anyway, as the rolling elements, balls such as steel balls are used, andsuch balls are supported in point contact state, and are hence small inload capacity and inferior in durability, and they cannot withstandlong-term use in the conditions of high speed and high load, and haveproblems in the service life.

In this regard, as shown in FIG. 4, a scroll type compressor havingplural double tapered rolling elements (double tapered rollers) asthrust force support structure has been proposed.

The scroll structure of the compressor is characterized, as shown in thedrawing, by fixing a fixed scroll member (c) having a volute body (b) ina housing (a), supporting a swirl scroll member (e) having a volute body(d) engaged with the volute body (b) so as to be free to swirl orrevolve by means of a thrust force support structure (f), and drivingand coupling the swirl scroll member (e) to a drive source not shownthrough a drive shaft (h) having a crankpin (g).

This support structure (f) is formed as a kind of thrust bearing asmentioned above, and a plurality of double tapered rollers R, R, . . . ,are interposed between a pair of parallel bearing races (i), (j) so asto be free to roll. The double tapered rollers R are held in a pair ofpockets provided oppositely to the bearing races (i) and (j),respectively (see, for example, Japanese Laid-open Patent No. 62-274113,Japanese Laid-open Patent No. 7-119741).

By rotary driving of the crankpin (g), the swirl scroll member (e)swirls or rotates without revolving on the fixed scroll member (c), andthe fluid gas sucked in from a suction port (not shown) is compressed ina compression chamber formed between the volute bodies (b, d), anddischarged from a discharge port (not shown)

In this case, the double tapered rollers R captured in the pockets ofbearing races (i, j) make rolling motions in the pockets to assurerelative and smooth swirl of the both bearing races (i, j), and arrestrelative rotation of both bearing races (i, j) (rotation of swirl scrollmember (e)).

In the thrust force support structure (f) using such double taperedrollers R, R, . . . , as compared with the conventional rolling elementsmade of spherical bodies, the durability is improved by far, and it ispossible to withstand high seed and heavy load for a longer period.

In spite of such excellent durability, the assembling and manufacturingtechnology of such thrust force support structure (f) is notestablished, and, in addition, the double tapered roller R itself has aspecial shape as compared with other conventional rolling elements, andit is not completed sufficiently as the rolling element for bearing.Hence, the scroll type compressor having the thrust force supportstructure (f) using double tapered rollers R is not put in practical useyet.

That is, the general shape of double tapered roller R, as shown in FIG.5(a), has a pair of conical or tapered surfaces Ra, Rb, and corners ofdouble tapered roller R (that is, both ends of generators of conicalsurfaces Ra, Rb) Rc, Rd are formed in a round shape, but in such shape,an edge load due to load at both ends of the section straight line(generator) is generated, and the contact stress with the bearing races(i,j) becomes excessive (see FIG. 5(b)).

For example, in FIG. 5(a), when the length L of double tapered roller Ralong the generator of conical or tapered surfaces Ra, Rb is 4.8 mm, thelength l₁ of corners Rc, Rd is 0.5 mm, and the apex angle θ is 90°, byapplying a thrust load to the bearing by 50 kgf per piece of doubletapered rollers, the edge load occurring at the small end side of thesection straight line is known to reach about 500 kgf/mm².

The invention is devised in the light of such problems of the prior art,and it is hence an object thereof to present double tapered rollershaving a structure of assuring an appropriate contact stress with thebearing races, without causing edge load due to load at both ends of thesection straight line on the conical surfaces.

SUMMARY OF THE INVENTION

To achieve the object, the double tapered roller of scroll thrustbearing of the invention is characterized in that a conical body has apair of conical or tapered surfaces matched coaxially and coupled atbottoms mutually, and the entire surface of the pair of conical surfacesis processed by crowning.

In a preferred embodiment, the outer contour shape of the crowning is anarc shape having a single radius of curvature along the overall lengthof the generator of the conical surface, and the radius of curvature ofthe arc shape is set at 100 times or less of the generator length of theconical surface.

The invention is based on the results of various preceding tests andstudies by the present inventor.

First, the inventor noticed that the cylindrical surface of thecylindrical roller was generally processed by crowning hitherto in orderto prevent generation of edge load due to load at both ends of thesection straight line (generator) (for example, Japanese Laid-openPatent No. 59-69519, Japanese Laid-open Utility Model No. 2-141723,Japanese Laid-open Patent No. 4-60215).

That is, as shown in FIG. 6, the conical or tapered surfaces Ra, Rb ofthe double tapered roller R were processed by crowning C₁, C₁ same as inthe cylindrical surface of cylindrical roller. In this shape, however,generation of edge load at both ends of the section straight line(generator) was eliminated, but the tendency of increase of contactstress at the apex side was not improved.

For example, in FIG. 6, in the case of the length L of the doubletapered roller R along the generators of the conical surfaces Ra, Rb of4.8 mm, the length l₁ of the corners Rc, Rd of 0.4 mm, the length l₂ ofcrowning C₁ of 0.2 mm, and the apex angle θ of 90°, when a load of 50kgf was applied per piece of double tapered rollers, the maximum contactstress at the small end side of the section straight line was found toreach about 300 kgf/mm² (the allowable maximum contact stress being 250kgf/mm²)

On the basis of such results, further tests and studies were continued,and the invention having such constitution is realized.

In the invention, since the entire surface of the pair of conical ortapered surfaces is processed by crowning, that is, full-crowning isprocessed, edge load is not generated at both ends of the sectionstraight line of the conical surfaces, and the contact stress at theapex side can be suppressed to a low value within an allowable range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view showing a double tapered roller of a scrollthrust bearing in embodiment 1 of the invention.

FIG. 2 is a diagram showing the maximum contact stress on the bearingrace of the conical surface of the double tapered roller.

FIG. 3 is a front view showing a double tapered roller of a scrollthrust bearing in embodiment 2 of the invention.

FIG. 4 is a front sectional view showing a thrust force supportstructure of a scroll type compressor in which the thrust roller bearingis applied.

FIG. 5 shows a conventional double tapered roller used in the thrustforce support structure, FIG. 5(a) being a front view and FIG. 5(b)being a diagram showing the maximum contact stress to the bearing raceof the conical surface.

FIG. 6 is a diagram showing the maximum contact stress on the bearingrace of the conical surface, by crowning the double tapered roller sameas in the cylindrical roller.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings, preferred embodiments of the inventionare described in detail below.

Embodiment 1

A double tapered roller of a scroll thrust bearing of the invention isshown in FIG. 1, in which the double tapered roller R is specificallyused in a thrust bearing preferably used as a thrust force supportstructure in a scroll type compressor, for example, as shown in FIG. 4.

The double tapered roller R is a conical body having a pair of conicalor tapered surfaces Ra, Rb matched coaxially and coupled at the bottomsmutually, and the corners of the double tapered roller R, that is, theapex of the double tapered roller R and boundaries Rc, Rd of the bothconical or tapered surfaces Ra, Rb are spherical surfaces.

The both conical surfaces Ra, Rb are rolling surfaces being finished bypolishing, and the apex angle of the both apices (geometrical apex) ofthe double tapered roller R, that is, the conical angle θ is 90°, andhence the intersection angle of the both conical surfaces Ra, Rb is alsoset at 90°.

The generator length of the conical surfaces Ra, Rb, that is, the lengthL of the conical surfaces Ra, Rb is set equal to the scroll radius inthe scroll type compressor be assembled in, and the entire surface ofthe conical surfaces Ra, Rb is processed by crowning C.

The outer contour shape of crowning C is an arc shape having a singleradius of curvature along the overall length of the generator of theconical surfaces Ra, Rb, and the radius of curvature r_(c) (see FIG. 2)of this arc shape is preferably set at 100 times or less of thegenerator length L of the conical surfaces Ra, Rb. For example, if thegenerator length L of the conical surfaces Ra, Rb is 4.8 mm, the radiusof curvature r_(c) of crowning C is set at 480 mm or less, for example,about 300 mm.

In thus constituted double tapered roller R, between both bearing plates1, 2, one conical surface Ra rolls on the raceway 1 a of the bearingrace 1, and other conical surface Rb rolls on the raceway 2 a of thebearing race 2.

In the double tapered roller R of the embodiment, the contact stresswith the bearing races 1, 2 was investigated.

The sample of the double tapered roller R is shown in FIG. 2, in whichthe length L of the double tapered roller along the generator of theconical surfaces Ra, Rb is 4.8 mm, the length l₁ of corners Rc, Rd is0.5 mm, the radius of curvature r_(c) of arc shape of crowning C isabout 300 mm, and the apex angle θ is 90°.

A plurality of double tapered rollers R in such standard dimensions werearranged between the pair of bearing plates 1, 2, and a thrust load wasapplied to this thrust bearing by 50 kgf per piece of double taperedrollers R, and, as a result, the maximum contact stress at the small endside in the contact region l₃ of the section straight line was bout 200kgf/mm², which was proved to be within an allowable range (allowablemaximum contact stress 250 kgf/mm² or less).

Embodiment 2

This embodiment is shown in FIG. 3, in which the double tapered roller Rof the embodiment is designed so that the load applied to the conicalsurfaces Ra, Rb may be biased to the large end side of the conicalsurface in a state being assembled in a scroll thrust bearing.

More specifically, the apex angle θ of the double tapered roller R isset at 80° to 85°, in order words, the relation between oscillationradius r of the scroll thrust bearing and swirl radius r₀ of doubletapered roller R is set at r₀=0.98 r to 0.998 r.

Herein, the oscillation radius r of the scroll thrust bearing refers tothe eccentricity of the crankpin (g) to the drive shaft (h) foroscillating the scroll thrust bearing, and the swirl radius r₀ of thedouble tapered roller R refers to the radius of the circle drawn by theapex (geometrical apex) of one conical surface Ra or Rb when otherconical surface Rb or Ra of the conical body for composing the doubletapered roller R rolls on a plane.

In thus constituted double tapered roller R, as shown in the drawing,between the both bearing plates 1 and 2, one conical surface Ra rolls onthe raceway 1 a of the bearing race 1, and other conical surface Rbrolls on the raceway 2 a of the bearing race 2, and when the bearing isassembled, the load applied to the conical surfaces Ra, Rb is biased tothe large end side of the conical surfaces Ra, Rb, and as compared withthe double tapered rollers of embodiment 1, it is more effective toprevent the peak of the maximum contact stress from concentrating at theapex side.

The other constitution and action are same as in embodiment 1.

The foregoing embodiments 1 and 2 are preferred examples of theinvention, and the invention is not limited to them alone, but may bechanged and modified in various designs within the scope thereof.

For example, the specific crowning shape of the double tapered roller Ris not limited to the illustrated embodiments alone as far as the abovebasic conditions are satisfied (the radius of curvature r_(c) of arcshape of crowning is 100 times or less of the generator length ofconical surfaces Ra, Rb, the apex angle θ of conical body is 90° orless)

INDUSTRIAL APPLICABILITY

As described herein, the double tapered roller of the invention is aconical body having a pair of conical surfaces matched coaxially andcoupled at bottoms mutually, and since the entire surface of the pair ofconical surfaces is processed by crowning, that is, full-crowning, edgeload due to load is not generated at both ends of the section straightline in the pair of conical surfaces, and the contact stress with thebearing race at the apex is controlled at an appropriate value withinthe allowable range.

Therefore, a completed double tapered roller as a rolling element forbearing is presented, and the scroll thrust bearing using double taperedrollers can be practically realized, so that its excellent durabilitymay be effectively exhibited.

In particular, as measure for improvement of the recent globalenvironments, the scroll type compressor is intensively developed as theproduct applicable to propane or other refrigerant, replacing theconventional chlorofluorocarbons, and the scroll thrust bearing usingthe double tapered rollers of the invention is excellent in durability,and withstands high speed and heavy load for a longer period, and henceit is ideal as the thrust force support structure of the scroll swirlunit in this kind of compressor. Therefore, the scroll thrust bearingfor thrust force support structure having double tapered rollers,hitherto being delayed in development, and the scroll type compressorcomprising such support structure may be put in practical use, andmanufactured in mass production.

What is claimed is:
 1. A double tapered roller of scroll thrust bearingbeing used as a rolling element of a thrust bearing interposed betweenpositions making relative scroll motions, comprising: a conical bodyhaving a pair of conical surfaces matched coaxially and coupled atbottoms mutually, wherein an entire surface of said pair of conicalsurfaces is processed by crowning, an outer contour shape of saidcrowning is an arc shape having a single radius of curvature alongsubstantially an overall length of a generator of said conical surfacesand the radius of curvature of the arc shape of said crowning is set at100 times or less of a generator length of the generator of said conicalsurfaces.
 2. The double tapered roller of scroll thrust bearing of claim1, wherein an apex angle of said conical body is set at 90° or less. 3.The double tapered roller of scroll thrust bearing of claim 1, wherein aload applied to said conical surfaces is biased to a large end side ofthe conical surfaces in a state being assembled in the scroll thrustbearing.
 4. The double tapered roller of scroll thrust bearing of claims3, wherein a relation between an oscillation radius r of the scrollthrust bearing and a swirl radius r₀ of said conical body as definedbelow is set in a range of r₀ =0.98 r to 0.998 r, wherein theoscillation radius r connotes an eccentricity of a drive shaft foroscillating the scroll thrust bearing and the swirl radius r₀ connotes aradius of a circle drawn by a geometrical apex of one conical surfacewhen the other conical surface of the conical body rolls on a plane. 5.The double tapered roller of scroll thrust bearing of claim 1, whereinan apex angle of said conical body is set at 80° to 85°.